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Enhancements in Lunar Radiance Calibration Using CERES and GERB Measurements

This presentation discusses the advancements in calibrating lunar radiance, essential for improving the accuracy of satellite instruments like CERES and GERB. Using the stable nature of the Moon as a calibration source, we examine how factors such as lunar phase, libration, and spectral differences from Earth scenes affect measurements. The ROLO model provides additional insights through spectral measurements, contributing to better characterizations of lunar brightness and radiance. Recommendations for future measurements of the Moon are also presented to enhance calibration efforts.

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Enhancements in Lunar Radiance Calibration Using CERES and GERB Measurements

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  1. Lunar Measurements with GERB Lou Smith Robert B. Lee, III GIST 18 Valencia, Espana Langley Research Centre

  2. Phase Angle Effects and Spectrum GIST 18 Valencia, Espana Langley Research Centre

  3. Libration of the Moon GIST 18 Valencia, Espana Langley Research Centre

  4. Libration Effects on Brightness GIST 18 Valencia, Espana Langley Research Centre

  5. Use of CERES to Calibrate the Moon • Lunar Radiance is not known accurately enough to be useful to CERES • However, the Moon is very stable and is considered as a calibration source for other instruments. • We are presently using CERES to help calibrate the Moon. GIST 18 Valencia, Espana Langley Research Centre

  6. Moon in CERES Pixel GIST 18 Valencia, Espana Langley Research Centre

  7. CERES/TRMM Measurementsof Lunar Shortwave Radiance GIST 18 Valencia, Espana Langley Research Centre

  8. CERES/TRMM Measurementsof Lunar Total Radiance GIST 18 Valencia, Espana Langley Research Centre

  9. CERES/TRMM WindowChannel Lunar Radiance GIST 18 Valencia, Espana Langley Research Centre

  10. GERB/Moon Measurements:Factors to Consider • The Moon differs spectrally from Earth Scenes and requires suitable spectral factors to unfilter measurements. • The Moon is a Non-uniform Target. • The Phase of the Moon has a strong effect. • Lunar Libration is Important. GIST 18 Valencia, Espana Langley Research Centre

  11. Distances Involved GERB Pixel Size = 1.2 milliradian MSG to Earth Centre = 42000 km Earth-Moon Distance = 384400 km Earth Moon MSG-1 MSG to Moon = 426400 km GIST 18 Valencia, Espana Langley Research Centre

  12. GERB View of Moon Moon’s Diameter = 6.6 GERB Pixels GIST 18 Valencia, Espana Langley Research Centre

  13. The Moon’s Orbit is Inclined5o to the Ecliptic • Due to Inclination of Moon relative to Earth’s Equator, from month to month, different Detectors will be viewing different Regions of the Moon. • The Calibration of each Detector must be known very well. GIST 18 Valencia, Espana Langley Research Centre

  14. Scanning of Moon by Different GERB Detectors Due to Orbit Inclination of Moon and Earth Spin Axis, The Moon will be viewed by Different Detectors over a Period of Time GIST 18 Valencia, Espana Langley Research Centre

  15. The ROLO Model:RObotic Lunar Observatory • Commissioned by Earth Observation System Program to Establish Moon as a Calibration Source. • People: Hugh Kieffer, Tom Stone (USGS)… • Located at Flagstaff, Arizona. • Telescope makes spectral measurements .35 to 2.5 m every night possible with CCD Array 512x512. GIST 18 Valencia, Espana Langley Research Centre

  16. ROLO Model • Atmospheric Corrections made. • Use Spectral Measurements over many Phase Angles to infer Lunar Map of Spectral BRDFs. • BRDFs described by Hapke’s Model with Parameters determined by Data. • Shortwave Radiances Accurate to 5-10%. • There is no Longwave Model. GIST 18 Valencia, Espana Langley Research Centre

  17. CERES and GERBContributions to Lunar Characterization • CERES will measure Shortwave Radiances from total Lunar Disc to help reduce ROLO Error Band. • CERES will measure Longwave Radiances from Total Lunar Disc. • GERB will Map Shortwave Radiance over Lunar Disc to help ROLO Model. • GERB will Map Longwave Radiances over Lunar Disc. GIST 18 Valencia, Espana Langley Research Centre

  18. Recommendation • GERB should make “measurements of opportunity” of Moon when it is in FOV near Earth within 5 days of Full Moon. GIST 18 Valencia, Espana Langley Research Centre

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